The drilling of oil wells necessitates running thousands of feet of drill string down to a borehole forming bit, and the cuttings from the bit are removed by circulating drilling fluids down through the string to the bit and back up the borehole annulus to the surface of the earth. In order to prevent blowouts should a high pressure formation be encountered, and in order to continue drilling after penetrating such a high pressure formation, it is necessary to seal the top of the well casing respective to the drill string. Therefore, the rotating kelly which drives the drill string is sealingly engaged by a rotating blowout preventor which isolates the annulus formed between the borehole and the drill string from ambient.
It is customary to drive the rotating part of the rotating blowout preventor with a kelly drive bushing which is attached to the uppermost end of the rotating blowout preventor. A stripper rubber is usually affixed to the lower rotating part of the rotating blowout preventor and sealingly engages the kelly in a telescoping or slidable manner.
Accordingly, the rotating blowout preventor is continuously contacted by the mud; and therefore, the various bearings, seals, and other moving parts wear rapidly and will soon deteriorate in this harsh environment.
It would therefore be desirable to have made available a rugged rotating blowout preventor which has the bearings thereof sealed in such a manner that they avoid contact with foreign debris and accordingly enjoy a long life, so that the bearings and seals do not usually need replacement during the borehole forming operation.